Oxygen Scavenger (Carbohydraside) Residual in Boiler Feed Water

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Hello Everyone, 

Could anybody advice what is the recomended Oxygen Scavenger (Carbohydraside) Residual in Boiler Feed Water.

much appreciated

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3 Answers

  1. Carbohydrazide (N2H3)2CO is a derivative of Hydrazine that decomposes under boiler feedwater conditions to form Hydrazine and Carbon Dioxide

    Based on the molar ratio, Carbohydrazide would be fed at 1.4:1 to Oxygen, but is normally used at a 2:1 ratio.  It is controlled by maintaining a residual of 20 to 60 ppb in the boiler feedwater.

     

    The advantages of using Carbohydrazide are the benefits of not adding TDS to the boiler system and avoiding the health risks related to Hydrazine.

    The disadvantage is Carbohydrazide cannot be used in systems below 9 bar due to the decomposition requirements.  Another disadvantage is residual Hydrazine in the feedwater can still break down into Ammonia potentially corroding any Copper alloys in the system.  An additional disadvantage is the Carbon Dioxide formed will carry over into the steam forming Carbonic Acid in the condensate. 

  2. 100-200 ppb of residual is enough. There are 2 factors:

    • You have to be sure that there is residual in water
    • You have to avoid overdosing (to save money)

    And as Terry said iron content is a good indicator of correct treatment. So if you have for example 50 ppb of oxygen scavenger and 0 ppb of iron it is enough for your system and your scavenger.

  3. The answer is somewhat complex and varies with operations.  We have a patented product that is a blend with carbohydrazide and we have a simple way in which we feed it and I'd assume you could use this same method. We start the feed at 10 times the DO content. So 10ppb DO, the starting feed would be 100ppb of our product.  We then monitor Fe and Cu levels.  Once these drop to ND, we will lower the feed of the product by 10% every 3 weeks until Fe or Cu values rise to detectible. Then we increase it 5%.  The only reason you are feeding the scavenger is to stop the corrosion and not seeing either metal would indicate you have stopped corrosion. Dosage doesn't tell you what your system needs, you system will tell you. Hope this helps.

    1 Comment

    1. Thank you for your answer, I just want to know that, is there any industrial guidline of the Carbohydraside residual in Boiler Feed Water.

      Currently we are using, 12% Carbohydraside product & only 0.15 ppm carbohydraside residual present.